RFID tags must have three basic elements: a chip, an antenna and the substrate. The substrate can be one of a variety of both flexible and rigid materials. This includes FR4 laminate (used in printed circuit boards), polyester and paper, among others. The antenna is a metallic based material and is produced on the substrate through either additive processes such as printing or deposition, or subtractive processes such as etching. The chip is a silicon integrated circuit (IC) that is attached to the antenna via solder or adhesive. Together, these three components form what is commonly called an inlay. The inlay itself can act as an RFID tag or it can be processed further to provide more robust capabilities for specialized applications. Examples of this additional processing include encapsulation in plastics or insertion under a label stock to produce a combination barcode/RFID smart label.
Various types of tags are needed for use in different environmental conditions. For example, tags that perform well when attached to cardboard cases may not be the best choice for wooden pallets, metal containers or glass. Tags may be as small as a grain of rice, as large as a brick, or thin and flexible enough to be embedded within an adhesive label and run through a bar code label printer. Tags also vary greatly by their performance, including read/write ability, memory and power requirements. Depending upon the application and environment, RFID tags have a range of durability. Paper-thin labels, often referred to as “smart labels” are typically used for disposable applications and, as such, are not as durable (Figure 4).
Many tags are used for permanent identification applications and can be encased in materials to withstand extreme environments or caustic materials that make text, bar code or other optical-based identification technologies unusable. RFID tags can be reusable and suitable for lifetime identification, which can provide a total cost of ownership (TCO) advantage over bar code labels or other identification methods that are disposable and need periodic replacement.
Tags are either
- passive, which receive their power from the signal sent by the reader,
- active, which have a battery to power their own transmissions, or,
- battery assisted, which have a battery that powers chip electronics but does not transmit RF energy.
Most current and proposed retail and consumer goods logistics RFID applications can be satisfied with passive tags, which are less expensive and smaller than active versions because they do not require a battery. Active tags are the best selection when the most important consideration is to be able to read the tags at the longest possible distance. Just like compact disks, RFID tags can be read-only or read-write.